March 8, 2007 – Because they don't eat less, people who get extra "liquid calories" from soft drinks gain extra weight, an analysis of 88 soda studies suggests.
The finding comes from researchers at the Rudd Center for Food Policy and Obesity at Yale University. Study co-author Marlene B. Schwartz, PhD, is research director of the Rudd Center.
"We found quite a clear association between soft-drink intake and taking in more calories," Schwartz tells WebMD. "The most compelling studies showed that, on days when people drink soft drinks, they consumed more calories than on the days when they did not have soft drinks."
Why? Schwartz says the simplest explanation is that people don't compensate for the extra calories in sodas. A person who has a hamburger and a soda, for example, doesn't eat less of his or her hamburger -- or fewer fries -- than a person who washes the burger down with water.
Some studies suggested that the fattening effects of soft drinks go beyond mere calorie counts.
"Sometimes, in fact, people who regularly drank soft drinks ate even more," Schwartz says. "The number of additional calories they took in was more than the calories in their soft drinks. It is almost as if sodas led to greater calorie intake because people get calibrated to a certain level of sweetness."
The Yale team looked at 88 different studies of nutrition and soft drinks. They then used a statistical technique for comparing the effects of soda drinking across all of the studies.
Since diets differ widely, it's hard to identify any single dietary factor that has even a small effect on health. Yet the Yale study shows that soft drinks have a "moderate" effect on calorie intake.
"If you are going to pick one change to make in your diet, and you drink sugared soft drinks, that would be a great place start," Schwartz says.
The study appears in the April 2007 issue of the American Journal of Public Health.
Soft Drinks Just Another Food Choice?
Barry M. Popkin, PhD, director of the obesity program at the University of North Carolina at Chapel Hill, was not involved in the Yale study. His own research suggests that soft-drink intake contributes to obesity.
"This was a very well done, careful study," Popkin tells WebMD. "It highlights ... the effects of sugared beverage intake on health."
Richard Adamson, PhD, a former NIH researcher, now serves as scientific consultant to The American Beverage Association, the trade group representing the U.S. soft-drink industry. His take on the Yale study is far different from that of Popkin.
Adamson says the Yale researchers did not include important studies that do not implicate soft drinks in obesity. He therefore wonders whether the authors cherry-picked studies and study data that support a preconceived conclusion.
And he says the study certainly does not prove that calories from soft drinks are more dangerous than calories from other foods.
"The idea that drinking liquid calories is different than eating solid calories is debatable," Adamson tells WebMD. "There are studies that show it is calorie intake that is important. It has nothing to do with whether foods are in a liquid or solid form."
If she seems to be picking on the soft-drink industry, Schwartz says, it's "because we really feel the science is there."
She notes that U.S. soft drink consumption has grown along with the U.S. obesity epidemic. In 1970, Americans drank 22 gallons of nondiet soft drinks per person. By 1997, that nearly doubled to 41 gallons per person -- and obesity went up 112%.
Tracey Halliday, a spokesperson for the American Beverage Association, says there's nothing wrong with choosing a soft drink for refreshment -- if it's part of an otherwise healthy lifestyle.
"It comes down to balancing calories consumed vs. calories burned," Halliday tells WebMD. "The beverage industry provides a range of choices, from bottled waters to sugared beverages, and all of them can be part of a healthy lifestyle. Adults can make healthy choices, and sugared beverages can be part of that."
Schwartz insists that sugared soft drinks aren't just another beverage.
"The message that soft drinks are not healthy beverages has been obscured by the industry rhetoric that any food can fit into a healthy diet," she says. "Our paper shows that all beverages are not equal."